Meaning
Physical defect characterized by the formation of localized, dome-shaped swellings or bubbles on the surface of battery electrodes, current collectors, or protective coatings indicates internal material separation. This defect, referred to as surface blistering, occurs when trapped gases or volatile solvents expand under heat or vacuum, forcing the surface layer to delaminate. It reduces the surface contact area and increases the electrical resistance of the affected component.
Defect Mechanism
During the drying step of the electrode coating process, if the oven temperature is too high, the solvent evaporates too rapidly and becomes trapped beneath the skin of the active material. The pressure of this trapped vapour rises until it forces the wet slurry to lift away from the copper or aluminum current collector foil. This results in empty pockets that reduce the adhesion strength of the active layer, causing eventual peeling.
Sourcing Selection
Component specifications for coated electrodes and separator foils use visual and mechanical peel tests to ensure that shipments are free from this defect. Sourcing teams reject batches that show any evidence of blistering, as these regions are highly prone to peeling and can cause short circuits. This verification reduces the risk of cell failure during the high-speed roll-to-roll assembly phase.
Pre-drying Requirement
Proper solvent extraction must be verified before high-vacuum steps to ensure that residual volatile compounds do not trigger localized lifting. Cells must be dried and evaluated before this vacuum cycle to avoid damaging the active material.
